Magnon-mediated qubit coupling determined via dissipation measurements
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2024-01-02 |
| Journal | Proceedings of the National Academy of Sciences |
| Authors | Masaya Fukami, Jonathan C. Marcks, Denis R. Candido, Leah R. Weiss, Benjamin Soloway |
| Institutions | University of Iowa, Eindhoven University of Technology |
| Citations | 22 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Magnon-Mediated Qubit Coupling
Section titled āTechnical Documentation & Analysis: Magnon-Mediated Qubit CouplingāExecutive Summary
Section titled āExecutive SummaryāThis research successfully characterizes the magnon-mediated coupling between Nitrogen-Vacancy (NV) centers in diamond and Yttrium Iron Garnet (YIG), providing a critical foundation for hybrid quantum systems (HQSs) and long-distance qubit entanglement.
- Core Achievement: Experimental determination of the magnon-induced self-energy ($\chi = \chiā + i\chiā$) of NV centers interfaced with YIG at room temperature (299.6 K).
- Methodology: Combines longitudinal relaxometry ($T_1$ measurements) with the fluctuation-dissipation and Kramers-Kronig relations to extract both the imaginary ($\chiā$, dissipation) and real ($\chiā$, coupling shift) components of the self-energy.
- Key Result: The real part of the self-energy provides an upper-bound estimate for the magnon-mediated NV-NV coupling strength, quantified as $g_{eff} \approx 2\pi \times 2$ Hz.
- Material Requirement: The experiment relies on high-quality, 100 Āµm thick Single Crystal Diamond (SCD) with NV centers implanted at a shallow depth ($h_{NV} \approx 7.7$ nm) to maximize coupling to the surface magnons (MSSWs).
- Significance for QIP: This room-temperature characterization technique simplifies the study of weakly coupled HQSs, informing future efforts to engineer entangled solid-state systems without requiring millikelvin temperatures.
- 6CCVD Value Proposition: 6CCVD specializes in providing the high-purity, custom-dimension SCD substrates (Ra < 1 nm) necessary to replicate and extend this research, particularly for achieving the long coherence times required for high cooperativity.
Technical Specifications
Section titled āTechnical SpecificationsāThe following hard data points were extracted from the research paper detailing the physical parameters and experimental results:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Material | SCD (Sumitomo) | N/A | 100 Āµm thick slab, laser cut |
| YIG Film Thickness | 3 | Āµm | Grown on 500 Āµm GGG substrate |
| NV Center Implantation Depth | 7.7 $\pm$ 3.0 | nm | Approximate depth from bottom surface |
| Calibrated NV-YIG Distance ($h_{NV}$) | 400(5) | nm | Used for theoretical modeling |
| Operating Temperature (T) | 299.6(3) | K | Room temperature |
| NV Zero-Field Splitting ($D_{NV}$) | $2\pi \times 2.87$ | GHz | NV center transition frequency |
| YIG Saturation Magnetization ($M_s$) | 1,716 | G/$\mu_0$ | Fitted parameter consistent with literature |
| Estimated NV-NV Coupling ($g_{eff}$) | $2\pi \times 2$ | Hz | Upper-bound estimate from $\chiā$ |
| Maximum Self-Energy Ratio $ | \chiā/\chiā | $ | 2.5 |
| Measured Ramsey Time ($T_2^*$) | $\approx 180$ | ns | Limited by nearby P1 centers |
| Projected Cooperativity ($C_{proj}$) | $\approx 2 \times 10^{-2}$ | N/A | Projected value assuming $T_2^* \approx 1$ ms |
Key Methodologies
Section titled āKey MethodologiesāThe experimental determination of the magnon-mediated coupling relied on precise material integration and advanced spin relaxometry techniques:
- Hybrid Structure Fabrication: A 100 Āµm Single Crystal Diamond (SCD) slab, containing implanted NV centers, was placed directly on top of a 3 Āµm YIG film grown on a Gadolinium Gallium Garnet (GGG) substrate.
- NV Axis Alignment: The diamond was laser cut such that one of the main NV symmetry axes (111) was parallel to the diamond/YIG surface, optimizing coupling geometry.
- Optical and Microwave Setup: Experiments utilized a confocal microscope for 532 nm laser initialization and PL readout. Pulsed microwave tones were applied via a copper wire placed over the sample.
- Longitudinal Relaxometry: Longitudinal relaxation rates ($\Delta(1/T_1)$) were measured by monitoring the differential PL signal of the $|m_s = 0\rangle \leftrightarrow |m_s = -1\rangle$ transition as a function of elapsed time ($t$).
- Dissipation Extraction ($\chiā$): The imaginary part of the self-energy ($\chiā$) was calculated directly from the measured relaxation rate $\Delta(1/T_1)$ using the fluctuation-dissipation relation: $\chiā(H) = \Delta(1/T_1) / [2 \cdot \text{coth}(\beta\omega_{NV}/2)]$.
- Coupling Shift Extraction ($\chiā$): The real part of the self-energy ($\chiā$), which provides the upper bound for $g_{eff}$, was calculated from the measured $\chiā$ data across the magnetic field sweep using the Kramers-Kronig relation.
6CCVD Solutions & Capabilities
Section titled ā6CCVD Solutions & Capabilitiesā6CCVD provides the specialized MPCVD diamond materials and engineering services required to replicate this foundational research and advance future NV-magnon HQS architectures, particularly those demanding higher coherence times and complex on-chip integration.
| Requirement from PNAS Paper | 6CCVD Solution & Capability | Technical Advantage |
|---|---|---|
| High-Purity Diamond Substrate (Essential for long $T_2^*$) | Optical Grade Single Crystal Diamond (SCD) | Our SCD material features ultra-low nitrogen concentration, minimizing P1 centers (the dominant decoherence source, $T_2^* \approx 180$ ns in the paper). This is critical for achieving the projected high cooperativity ($C_{proj}$) needed for practical quantum gates. |
| Custom Dimensions & Thickness (100 Āµm slab, laser cut) | SCD Plates/Wafers (0.1 Āµm - 500 Āµm) | We offer custom-cut SCD plates with precise thickness control (e.g., 100 Āµm) and custom dimensions up to 125mm (PCD), ensuring seamless integration with complex YIG/GGG heterostructures. |
| Optimal Surface Interface ($h_{NV}$ control) | Ultra-Polished SCD Substrates (Ra < 1 nm) | Achieving precise, shallow NV implantation (7.7 nm depth) requires an atomically smooth surface. 6CCVD guarantees surface roughness of Ra < 1 nm on SCD, optimizing the interface for maximal coupling to surface magnons (MSSWs). |
| Integrated Microwave Structures (Future HQS designs) | Custom Metalization Services (Au, Pt, Pd, Ti, W, Cu) | For scaling up to deterministic entanglement using integrated waveguides or nanobars (as discussed in Fig. 4D), 6CCVD offers in-house deposition of multi-layer metal stacks (e.g., Ti/Pt/Au) for fabricating high-performance microwave transducers directly on the diamond surface. |
| Engineering Support (Material selection, orientation) | In-House PhD Engineering Team | Our material scientists provide authoritative consultation on selecting the optimal diamond orientation (e.g., (111) vs. (100)), doping levels (BDD for conductivity), and surface preparation necessary to maximize NV-magnon coupling strength and minimize dissipation for specific HQS applications. |
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Controlled interaction between localized and delocalized solid-state spin systems offers a compelling platform for on-chip quantum information processing with quantum spintronics. Hybrid quantum systems (HQSs) of localized nitrogen-vacancy (NV) centers in diamond and delocalized magnon modes in ferrimagnetsāsystems with naturally commensurate energiesāhave recently attracted significant attention, especially for interconnecting isolated spin qubits at length-scales far beyond those set by the dipolar coupling. However, despite extensive theoretical efforts, there is a lack of experimental characterization of the magnon-mediated interaction between NV centers, which is necessary to develop such hybrid quantum architectures. Here, we experimentally determine the magnon-mediated NV-NV coupling from the magnon-induced self-energy of NV centers. Our results are quantitatively consistent with a model in which the NV center is coupled to magnons by dipolar interactions. This work provides a versatile tool to characterize HQSs in the absence of strong coupling, informing future efforts to engineer entangled solid-state systems.